Numerous studies have indicated the effectiveness of green tea for anti-cancer activity in both humans and experimental animals, and green tea extract has reached clinical trials for examination of its efficacy for anti- cancer therapy. Epigallocatechin-3-gallate (EGCG), the major catechin in green tea has been shown to be a primary component eliciting this biological activity. Several animal studies have shown EGCG to protect against a variety of cancers, both spontaneous and chemically induced. We made the novel discovery that EGCG is an inhibitor of the chaperone 90 kDa heat shock protein (hsp90). Our overall hypothesis is that the reported anti-cancer activity of EGCG is due, at least in part, to its ability to modulate hsp90 function. This hypothesis will be tested using a unique model of human prostate cancer in mice. As far as we are aware, this is the only such model undergoing human epithelial malignant transformation and metastasis using a hormone mix normally found in men, thus representing all stages of human carcinogenesis. Using in vivo and in vitro approaches with this model, we will determine whether differential sensitivity to EGCG will be observed as these epithelial cells progress from being non-tumorigenic, to transformed, to metastatic stages. Using the most sensitive stage, we will further determine in a concentration- and time-dependent manner whether EGCG modulates the levels and/or function of hsp90 client proteins, consistent with the notion that EGCG inhibits growth of prostate cancer cells through its ability to inhibit hsp90 activity. To further differentiate between hsp90-dependent effects and possible non-hsp90 effects, we will use an innovative proteomic approach that assess the ability of EGCG to affect a variety of signaling pathways.